In these days, ultra-fine processing techniques are required for production of semiconductor devices. Under such circumstances, dry etching processes are becoming the mainstream in place of wet processes. The dry etching process is a technique in which a fine pattern is formed on a molecule-by-molecule basis on a material surface by generation of a plasma in the vacuum.
For the etching of semiconductor material such as silicon dioxide (SiO2), perfluorocarbons (PFC) such as CF4, CHF3, C2F6, C3F8 and C4F8 and hydrofluorocarbons (HFC) have been used as etching agents in order to increase the etching rate of SiO2 relative to substrate material such as silicon, polysilicon or silicon nitride. However, the PFC and HFC gases are specified as emission control materials in the Kyoto protocol (COP3) because each of these PFC and HFC gases has a long atmospheric lifetime and a high global warming potential (GWP). There has been a demand for alternative low-GWP materials having high cost efficiency and capable of fine processing in the semiconductor industry.
Patent Document 1 discloses a method using a reactive gas containing a C4-C7 perfluoroketone as a cleaning gas or an etching gas. The disclosed reactive gas is not, however, always suitable as the etching gas due to the fact that a decomposition product of the perfluoroketone contains a high-GWP compound and a relatively high-boiling material.
Patent Document 2 discloses a method using a C2-C6 hydrofluoro ether (HFE) as a dry etching gas.
Against the above background, it has been demanded to develop compounds having lower GWP and easy to produce industrially. The application of an unsaturated fluorocarbon, which has a double or triple bond in the molecule, for etching process has been examined. As a technique relevant to such an application, Patent Document 3 discloses a method of etching a Si film, a SiO2 film, a Si3N4 film or a high-melting metal silicide with the use of an ether such as CaF2a+1OCF═CF2 or fluorinated olefin such as CF3CF═CFH, CH3CH═CH2 etc.
Patent Document 4 discloses a plasma etching method using hexafluoro-2-butyne, hexafluoro-1,3-butadiene, hexafluoropropene or the like as an etching gas.
Patent Document 5 discloses a method of etching an oxide layer on a non-oxide layer e.g. nitride layer with the use of a mixed gas containing: (a) an unsaturated fluorocarbon selected from the group consisting of hexafluorobutadiene, octafluoropentadiene, pentafluoropropene and trifluoropropyne; (b) a hydrofluoro methane selected from the group consisting of monofluoromethane and difluoromethane; and (c) an inert carrier gas.
Patent Document 6 discloses a method using a C5-C6 acyclic perfluoroalkyne as a plasma reaction gas.